        (SETQ 3dpolyobj (CAR (vlax-safearray->list (vlax-variant-value border))));get the 3D polyline object, (vlax-safearray->list ...) is easiest method I found.
        (SETQ 3dplpts (VLAX-GET 3dpolyobj 'Coordinates));get the 3D polyline coordinates list (these return in raw list form and not as point triplets).

  (setq ptsList 3dpolyobj)
  (setq arraySpace (vlax-make-safearray
              vlax-vbdouble ; element type
              (cons 0
                    (- (length ptsList) 1)
                    ) ; array dimension
              )
  )

  (setq sArray (vlax-safearray-fill arraySpace ptsList))

  ; return array variant
  (SETQ MyVariant (vlax-make-variant sArray))